Table 1 Descriptive statistics for health outcomes, meteorology and urban background pollutants in Copenhagen over 1327 study days (15 May 2001 to 31 December 2004)

	Days (n)	Mean (SD)	Percentiles				IQR*
	Days (n)	Mean (SD)	25th	50th	75th	99th	IQR*
Health outcome
CVD admissions (⩾65 years)	1327	59 (24)	35	65	77	103	42
RD admissions (⩾65 years)	1327	22 (9)	16	22	28	44	12
Asthma admissions (5–18 years)	1327	3 (2)	1	3	4	9	3
Meteorology
Temperature (°C)	1284	10 (7)	5	10	16	23	11
Relative humidity (%)	1284	73 (10)	66	74	82	93	16
Number concentration (particles/cm3)
NC†_tot	578	8116 (3502)	5738	7358	9645	19895	3907
NC_a12	578	493 (315)	308	463	650	1463	342
NC_a23	578	2253 (1364)	1280	2057	3066	6096	1786
NC_a57	578	5104 (2687)	3248	4562	6274	14410	3026
NC₁₀₀‡	578	6847 (2864)	4959	6243	8218	16189	3259
NC_a212	578	392 (441)	89	246	584	2248	495
Mass concentration (µg/m3)
PM₁₀	1169	24 (14)	16	21	29	72	13
PM_2.5	453	10 (5)	7	9	12	28	5
Gases (ppb)
CO	1230	290 (100)	220	260	340	610	120
NO₂	1245	11 (5)	8	11	14	28	6
NO_x	1245	15 (8)	9	12	18	46	9
O₃	493	24 (10)	18	24	30	48	12
NO_xKerbside§	1286	83 (36)	58	76	103	207	45

*IQR, interquartile range, difference between 75th and 25th percentile.
†NC, number concentration; tot, total (all particles 6–700 nm in diameter); a12, size mode with mean diameter of 12 nm; a23, size mode with median diameter of 23 nm; a57, size mode with median diameter of 57 nm; a212, size mode with median diameter of 212 nm.
‡NC₁₀₀ = a12+a23+0.797*a57+0.084*a212.
§NO_xKerbside, NO_x levels measured at kerbside monitor.